Looks like it could be a number of things but start with the most obvious which is tuning. Best thing to do when you're not sure is to start back at the beginning. Go back to factory settings (both screws flush with casing) and get it to idle. Next do high speed passes and tune the high speed needle till it goes as fast as you can get it to go, then back it down 1/8th turn. Next adjust the low speed be mashing the throttle from a stop till you get the desired effect. You'll probably need to adjust the idle as you go since, as you said the low speed and idle work together and have to be in harmony. Once you're done with the low speed, fine tune the idle and you should be good to go.
This being said you might have other problems as well. You could have an air leak on the engine (look it up) or your plug might not be the right one for your engine. One problem i had when i first started was i had the idle adjusted with a throttle that was held a tiny bit open by the servo and when i would brake it would die. Took me a while till i noticed this problem that had nothing to do with the engine. It doesnt look like you were braking so you can rule that out, its just an example of why you should never overlook anything.
Whatever you do dont pay someone to work on it for you. They overcharge, dont always do a great job and you learn nothing.
Good luck and welcome to the forum.